Illuminators are used in conjunction with video security cameras where and when the available light is insufficient for quality observation or recording of the subject scene. Examples of situations that would benefit from the use of an illuminator are unlit or partially lit parking lots, storage facilities, warehouses, office spaces, manufacturing facilities, and the like. These areas of interest for video observation include both indoor and outdoor spaces. For outdoor use, the security camera and the illuminator may be designed to be rugged and weatherproof
Illuminators used in video security applications may provide visible light, infrared (IR) light, or both. The electronic sensors used in modern video cameras are intrinsically sensitive to both visible light and infrared light. When ambient light (sunlight or artificial light) is available and abundant, video cameras typically employ an infrared blocking filter that prevents infrared light collected by the camera's lens from reaching the sensor. Reducing or eliminating the infrared light allows for more accurate color rendition in the video image. When there is not sufficient ambient light for good color imaging, it is advantageous to remove the infrared blocking filter so that both infrared and visible light reach the sensor. The resulting image may not be as color-accurate as an image taken using only visible light, but the greater amount of available light makes it possible to produce an image higher quality in other respects, for example an image with less noise.
These video cameras with so-called “day-night” capability greatly extend the range of conditions in which usable video images can be obtained. Still, there are many locations and situations where the available light is not sufficient. These installations benefit from the use of illuminators to augment the available light. The advantage if IR illuminators is that the illuminator adds light that is visible to the camera, but invisible (or nearly invisible) to humans. This may be advantageous for several reasons. For example, some installations are designed to be covert. That is, in these installations, it is not desirable that subjects in the field of the video camera are aware that they are being observed or recorded. Some regions or municipalities also limit the amount of visible artificial light that is used at night. The goal of such “Dark Sky” initiatives is to reduce light pollution so that people can enjoy the night sky. Other reasons for using infrared illuminators are simply the annoyance, distraction, and ergonomic factors associated with the use of additional visible light.
The range of wavelengths typically used for IR illuminators in conjunction with day/night cameras is referred to as “near infrared”. Two common wavelengths of light produced by IR illuminators are 850 and 940 nm, although other wavelengths or ranges of wavelengths could be used. Illuminators producing light at a wavelength of 850 nm are commonly used because video sensors are reasonably sensitive at this wavelength. The human eye is weakly sensitive at 850 nm, so the illuminator is not truly covert—it will be seen to glow a deep red color. Illuminators producing light at a wavelength of 940 nm are used for covert illumination, since the eye is insensitive at this wavelength. The primary disadvantage of 940 nm is that the sensitivity of typical visible light sensors is significantly lower at this wavelength.
Different security cameras may have different fields of view, and some security cameras include zoom lenses such that the field of view of the camera is variable. There is accordingly a need for improved illuminators useful with cameras of differing or variable fields of view.